Carbon is a material that can be deployed as a catalyst support or adsorbent. The most commonly used carbon based supports for chemical catalysis are activated carbons exhibiting high specific surface areas (e.g., over 500 m2/g). Preparing activated carbon requires activating a carbonaceous material such as charcoal, wood, coconut shell or petroleum-sourced carbon black either by a chemical activation, such as contacting with an acid at high temperatures, or by steam activation. Both methods of activation produce high concentrations of micropores and consequently higher surface areas. Depending upon the source of the carbonaceous material, the resultant activated carbons may have a high residual content of inorganic ash and sulfur, and possibly oxygen or nitrogen-containing functional groups at the surface. Activated carbons are thought to possess an optimum support structure for catalytic applications as they enable good dispersion of catalytically active components and effective adsorption and reaction of chemical reagents at the catalyst surface.
In recent years, there has been a growing interest in using biorenewable materials as a feedstock to replace or supplement crude oil. See, for example, Klass, Biomass for Renewable Energy, Fuels, and Chemicals, Academic Press, 1998. This publication and all other cited publications are incorporated herein by reference. One of the major challenges for converting biorenewable resources such as carbohydrates (e.g., glucose derived from starch, cellulose or sucrose) to current commodity and specialty chemicals is the selective removal of oxygen atoms from the carbohydrate. Approaches are known for converting carbon-oxygen single bonds to carbon-hydrogen bonds. See, for example, U.S. Pat. No. 8,669,397, which describes a process for the conversion of glucose to adipic acid via the intermediate glucaric acid. One challenging aspect associated with the catalytic conversions of highly functionalized biorenewably-derived molecules and intermediates is reaching the high levels of catalytic activity, selectivity and stability necessary for commercial applications. With respect to catalytic activity and selectivity, highly functionalized, biorenewably-derived molecules and intermediates derived from carbohydrates (e.g., glucose and glucaric acid) are non-volatile and must therefore be processed as solutions in the liquid phase. When compared to gas phase catalytic processes, liquid phase catalytic processes are known to suffer from lower productivities because liquid to solid (and gas to liquid to solid) diffusion rates are slower than gas to solid diffusion rates.
Another challenging aspect associated with the catalytic conversion of highly functionalized biorenewably-derived molecules and intermediates is the use of chemically aggressive reaction conditions. For example, U.S. Pat. No. 8,669,397 describes catalytic conversion steps performed at elevated temperatures in the presence of polar solvents such as water and acetic acid. Polar solvents are typically required for the dissolution of non-volatile, highly-functionalized molecules such as glucose and glucaric acid, and elevated temperatures are required for productive and affordable catalytic conversion steps for commodity chemical applications. Therefore, a significant challenge associated with the catalytic conversion of highly functionalized biorenewably-derived molecules and intermediates is catalyst stability. Long term catalyst stability is a necessity for commodity chemical production, meaning that the catalyst must be stable, productive, and selective under reaction conditions for long periods.
The challenges associated with the development of industrial shaped catalysts, especially in the conversion of biorenewably-derived molecules and intermediates, are a) high productivity and selectivity consistent with an economically viable catalyst at industrial scale, b) mechanical and chemical stability of the shaped catalyst support and c) retention of the catalytically active components by the support and the avoidance of leaching of the catalytically active components into a polar solvent reaction medium. There remains a need for industrially scalable, highly active, selective and stable catalyst supports and catalyst compositions that can satisfy these challenges.